Playing fast well requires a gradual ramp up in speed in manageable intervals from slow and steady, to fast and steady. This is what I've done for a few flamenco guitar techniques like rasgueo and picado runs, inspired by well-worn teaching methodologies. Pick up the book The Musician's Way, or read the Musician's Way blog if you get a chance.
How do you ramp up the speed without sacrificing quality of sound, tone, attack? Here's a little trick to do that when you work technique into your practice schedule.
Let's assume you've isolated a hurdle you are trying to work past, which to you is a problem related to speed, but could in fact be masking an underlying technical problem that needs to be worked into your muscles, strengthening them at a slower speed.
Find how you want to fit the speedy riff that was difficult into the metronome's time: 3/4, 4/4, etc.
Start at a comfortable speed on the metronome, probably somewhere under 100 bpm
Play the riff at least 5-10 times on the <100 bpm speed, listening to any inaccuracy of execution.
Speed up 10 bpm, play same thing 5-10 times, speed up 10 bpm, play the same, speed up 10 bpm play the same.
Take a break and put it down, or come back to it later. This should envigorate your practice, not wear it out.
What brings us back home?
This eternal questions always comes knocking on my skull, when I feel a certain rush to go back home, see my friends, hang out at my house, escape my house (which is just my parents' house now) walk across the seconds and be at my friends in a second, protected from the crush of criticism, parental guidance, and the silence and peace, which is my protector, but also troubling in a way -- being tucked away in a peaceful, quite place is something bizarre to me, an illusion, the impossible becoming real?
I look from parents yard at half the city and more, all the way toward Redondo Beach, lands I've visited but never stayed more than a night or two at friends' houses. Nobody over there would have me anymore.
It's a long trip anywhere in the city, but its millions of residences and microneighborhoods are like a feudal retreat from the anything goes anywhere of San Francisco, where seemingly you can't escape the madness, the madmen, the visionaries, the traffic, anywhere. You're always a few steps from the grittiness of the street. LA offers little retreats where vagabonds and madmen can't get you, stalk you to your doorstep, I suppose.
Making it is getting out of the rush, but not being so isolated as to forget people or let them forget you. If I could build something that assures people can dream: musical collaboration, community, friendships, I want to make this happen. If I do, I will have come out on top, leaving the rush not to escape, but to build something great.
Write, post, publish, prophet!